#define LLVM_TRANSFORMS_IPO_H
#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
namespace llvm {
/// to bitsets.
ModulePass *createLowerBitSetsPass();
+//===----------------------------------------------------------------------===//
+// SampleProfilePass - Loads sample profile data from disk and generates
+// IR metadata to reflect the profile.
+ModulePass *createSampleProfileLoaderPass();
+ModulePass *createSampleProfileLoaderPass(StringRef Name);
+
} // End llvm namespace
#endif
//
FunctionPass *createPartiallyInlineLibCallsPass();
-//===----------------------------------------------------------------------===//
-//
-// SampleProfilePass - Loads sample profile data from disk and generates
-// IR metadata to reflect the profile.
-FunctionPass *createSampleProfileLoaderPass();
-FunctionPass *createSampleProfileLoaderPass(StringRef Name);
-
//===----------------------------------------------------------------------===//
//
// ScalarizerPass - Converts vector operations into scalar operations
PartialInlining.cpp
PassManagerBuilder.cpp
PruneEH.cpp
+ SampleProfile.cpp
StripDeadPrototypes.cpp
StripSymbols.cpp
initializeStripNonDebugSymbolsPass(Registry);
initializeBarrierNoopPass(Registry);
initializeEliminateAvailableExternallyPass(Registry);
+ initializeSampleProfileLoaderPass(Registry);
}
void LLVMInitializeIPO(LLVMPassRegistryRef R) {
--- /dev/null
+//===- SampleProfile.cpp - Incorporate sample profiles into the IR --------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the SampleProfileLoader transformation. This pass
+// reads a profile file generated by a sampling profiler (e.g. Linux Perf -
+// http://perf.wiki.kernel.org/) and generates IR metadata to reflect the
+// profile information in the given profile.
+//
+// This pass generates branch weight annotations on the IR:
+//
+// - prof: Represents branch weights. This annotation is added to branches
+// to indicate the weights of each edge coming out of the branch.
+// The weight of each edge is the weight of the target block for
+// that edge. The weight of a block B is computed as the maximum
+// number of samples found in B.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/PostDominators.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DebugInfo.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/ProfileData/SampleProfReader.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/IPO.h"
+#include <cctype>
+
+using namespace llvm;
+using namespace sampleprof;
+
+#define DEBUG_TYPE "sample-profile"
+
+// Command line option to specify the file to read samples from. This is
+// mainly used for debugging.
+static cl::opt<std::string> SampleProfileFile(
+ "sample-profile-file", cl::init(""), cl::value_desc("filename"),
+ cl::desc("Profile file loaded by -sample-profile"), cl::Hidden);
+static cl::opt<unsigned> SampleProfileMaxPropagateIterations(
+ "sample-profile-max-propagate-iterations", cl::init(100),
+ cl::desc("Maximum number of iterations to go through when propagating "
+ "sample block/edge weights through the CFG."));
+
+namespace {
+typedef DenseMap<BasicBlock *, unsigned> BlockWeightMap;
+typedef DenseMap<BasicBlock *, BasicBlock *> EquivalenceClassMap;
+typedef std::pair<BasicBlock *, BasicBlock *> Edge;
+typedef DenseMap<Edge, unsigned> EdgeWeightMap;
+typedef DenseMap<BasicBlock *, SmallVector<BasicBlock *, 8>> BlockEdgeMap;
+
+/// \brief Sample profile pass.
+///
+/// This pass reads profile data from the file specified by
+/// -sample-profile-file and annotates every affected function with the
+/// profile information found in that file.
+class SampleProfileLoader : public ModulePass {
+public:
+ // Class identification, replacement for typeinfo
+ static char ID;
+
+ SampleProfileLoader(StringRef Name = SampleProfileFile)
+ : ModulePass(ID), DT(nullptr), PDT(nullptr), LI(nullptr),
+ Ctx(nullptr), Reader(), Samples(nullptr), Filename(Name),
+ ProfileIsValid(false) {
+ initializeSampleProfileLoaderPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool doInitialization(Module &M) override;
+
+ void dump() { Reader->dump(); }
+
+ const char *getPassName() const override { return "Sample profile pass"; }
+
+ bool runOnModule(Module &M) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.setPreservesCFG();
+
+ AU.addRequired<LoopInfoWrapperPass>();
+ AU.addPreserved<LoopInfoWrapperPass>();
+
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
+
+ AU.addRequired<PostDominatorTree>();
+ AU.addPreserved<PostDominatorTree>();
+ }
+
+protected:
+ bool runOnFunction(Function &F);
+ unsigned getFunctionLoc(Function &F);
+ bool emitAnnotations(Function &F);
+ unsigned getInstWeight(Instruction &I);
+ unsigned getBlockWeight(BasicBlock *BB);
+ void printEdgeWeight(raw_ostream &OS, Edge E);
+ void printBlockWeight(raw_ostream &OS, BasicBlock *BB);
+ void printBlockEquivalence(raw_ostream &OS, BasicBlock *BB);
+ bool computeBlockWeights(Function &F);
+ void findEquivalenceClasses(Function &F);
+ void findEquivalencesFor(BasicBlock *BB1,
+ SmallVector<BasicBlock *, 8> Descendants,
+ DominatorTreeBase<BasicBlock> *DomTree);
+ void propagateWeights(Function &F);
+ unsigned visitEdge(Edge E, unsigned *NumUnknownEdges, Edge *UnknownEdge);
+ void buildEdges(Function &F);
+ bool propagateThroughEdges(Function &F);
+
+ /// \brief Line number for the function header. Used to compute absolute
+ /// line numbers from the relative line numbers found in the profile.
+ unsigned HeaderLineno;
+
+ /// \brief Map basic blocks to their computed weights.
+ ///
+ /// The weight of a basic block is defined to be the maximum
+ /// of all the instruction weights in that block.
+ BlockWeightMap BlockWeights;
+
+ /// \brief Map edges to their computed weights.
+ ///
+ /// Edge weights are computed by propagating basic block weights in
+ /// SampleProfile::propagateWeights.
+ EdgeWeightMap EdgeWeights;
+
+ /// \brief Set of visited blocks during propagation.
+ SmallPtrSet<BasicBlock *, 128> VisitedBlocks;
+
+ /// \brief Set of visited edges during propagation.
+ SmallSet<Edge, 128> VisitedEdges;
+
+ /// \brief Equivalence classes for block weights.
+ ///
+ /// Two blocks BB1 and BB2 are in the same equivalence class if they
+ /// dominate and post-dominate each other, and they are in the same loop
+ /// nest. When this happens, the two blocks are guaranteed to execute
+ /// the same number of times.
+ EquivalenceClassMap EquivalenceClass;
+
+ /// \brief Dominance, post-dominance and loop information.
+ DominatorTree *DT;
+ PostDominatorTree *PDT;
+ LoopInfo *LI;
+
+ /// \brief Predecessors for each basic block in the CFG.
+ BlockEdgeMap Predecessors;
+
+ /// \brief Successors for each basic block in the CFG.
+ BlockEdgeMap Successors;
+
+ /// \brief LLVM context holding the debug data we need.
+ LLVMContext *Ctx;
+
+ /// \brief Profile reader object.
+ std::unique_ptr<SampleProfileReader> Reader;
+
+ /// \brief Samples collected for the body of this function.
+ FunctionSamples *Samples;
+
+ /// \brief Name of the profile file to load.
+ StringRef Filename;
+
+ /// \brief Flag indicating whether the profile input loaded successfully.
+ bool ProfileIsValid;
+};
+}
+
+/// \brief Print the weight of edge \p E on stream \p OS.
+///
+/// \param OS Stream to emit the output to.
+/// \param E Edge to print.
+void SampleProfileLoader::printEdgeWeight(raw_ostream &OS, Edge E) {
+ OS << "weight[" << E.first->getName() << "->" << E.second->getName()
+ << "]: " << EdgeWeights[E] << "\n";
+}
+
+/// \brief Print the equivalence class of block \p BB on stream \p OS.
+///
+/// \param OS Stream to emit the output to.
+/// \param BB Block to print.
+void SampleProfileLoader::printBlockEquivalence(raw_ostream &OS,
+ BasicBlock *BB) {
+ BasicBlock *Equiv = EquivalenceClass[BB];
+ OS << "equivalence[" << BB->getName()
+ << "]: " << ((Equiv) ? EquivalenceClass[BB]->getName() : "NONE") << "\n";
+}
+
+/// \brief Print the weight of block \p BB on stream \p OS.
+///
+/// \param OS Stream to emit the output to.
+/// \param BB Block to print.
+void SampleProfileLoader::printBlockWeight(raw_ostream &OS, BasicBlock *BB) {
+ OS << "weight[" << BB->getName() << "]: " << BlockWeights[BB] << "\n";
+}
+
+/// \brief Get the weight for an instruction.
+///
+/// The "weight" of an instruction \p Inst is the number of samples
+/// collected on that instruction at runtime. To retrieve it, we
+/// need to compute the line number of \p Inst relative to the start of its
+/// function. We use HeaderLineno to compute the offset. We then
+/// look up the samples collected for \p Inst using BodySamples.
+///
+/// \param Inst Instruction to query.
+///
+/// \returns The profiled weight of I.
+unsigned SampleProfileLoader::getInstWeight(Instruction &Inst) {
+ DebugLoc DLoc = Inst.getDebugLoc();
+ if (!DLoc)
+ return 0;
+
+ unsigned Lineno = DLoc.getLine();
+ if (Lineno < HeaderLineno)
+ return 0;
+
+ const DILocation *DIL = DLoc;
+ int LOffset = Lineno - HeaderLineno;
+ unsigned Discriminator = DIL->getDiscriminator();
+ unsigned Weight = Samples->samplesAt(LOffset, Discriminator);
+ DEBUG(dbgs() << " " << Lineno << "." << Discriminator << ":" << Inst
+ << " (line offset: " << LOffset << "." << Discriminator
+ << " - weight: " << Weight << ")\n");
+ return Weight;
+}
+
+/// \brief Compute the weight of a basic block.
+///
+/// The weight of basic block \p BB is the maximum weight of all the
+/// instructions in BB. The weight of \p BB is computed and cached in
+/// the BlockWeights map.
+///
+/// \param BB The basic block to query.
+///
+/// \returns The computed weight of BB.
+unsigned SampleProfileLoader::getBlockWeight(BasicBlock *BB) {
+ // If we've computed BB's weight before, return it.
+ std::pair<BlockWeightMap::iterator, bool> Entry =
+ BlockWeights.insert(std::make_pair(BB, 0));
+ if (!Entry.second)
+ return Entry.first->second;
+
+ // Otherwise, compute and cache BB's weight.
+ unsigned Weight = 0;
+ for (auto &I : BB->getInstList()) {
+ unsigned InstWeight = getInstWeight(I);
+ if (InstWeight > Weight)
+ Weight = InstWeight;
+ }
+ Entry.first->second = Weight;
+ return Weight;
+}
+
+/// \brief Compute and store the weights of every basic block.
+///
+/// This populates the BlockWeights map by computing
+/// the weights of every basic block in the CFG.
+///
+/// \param F The function to query.
+bool SampleProfileLoader::computeBlockWeights(Function &F) {
+ bool Changed = false;
+ DEBUG(dbgs() << "Block weights\n");
+ for (auto &BB : F) {
+ unsigned Weight = getBlockWeight(&BB);
+ Changed |= (Weight > 0);
+ DEBUG(printBlockWeight(dbgs(), &BB));
+ }
+
+ return Changed;
+}
+
+/// \brief Find equivalence classes for the given block.
+///
+/// This finds all the blocks that are guaranteed to execute the same
+/// number of times as \p BB1. To do this, it traverses all the
+/// descendants of \p BB1 in the dominator or post-dominator tree.
+///
+/// A block BB2 will be in the same equivalence class as \p BB1 if
+/// the following holds:
+///
+/// 1- \p BB1 is a descendant of BB2 in the opposite tree. So, if BB2
+/// is a descendant of \p BB1 in the dominator tree, then BB2 should
+/// dominate BB1 in the post-dominator tree.
+///
+/// 2- Both BB2 and \p BB1 must be in the same loop.
+///
+/// For every block BB2 that meets those two requirements, we set BB2's
+/// equivalence class to \p BB1.
+///
+/// \param BB1 Block to check.
+/// \param Descendants Descendants of \p BB1 in either the dom or pdom tree.
+/// \param DomTree Opposite dominator tree. If \p Descendants is filled
+/// with blocks from \p BB1's dominator tree, then
+/// this is the post-dominator tree, and vice versa.
+void SampleProfileLoader::findEquivalencesFor(
+ BasicBlock *BB1, SmallVector<BasicBlock *, 8> Descendants,
+ DominatorTreeBase<BasicBlock> *DomTree) {
+ for (auto *BB2 : Descendants) {
+ bool IsDomParent = DomTree->dominates(BB2, BB1);
+ bool IsInSameLoop = LI->getLoopFor(BB1) == LI->getLoopFor(BB2);
+ if (BB1 != BB2 && VisitedBlocks.insert(BB2).second && IsDomParent &&
+ IsInSameLoop) {
+ EquivalenceClass[BB2] = BB1;
+
+ // If BB2 is heavier than BB1, make BB2 have the same weight
+ // as BB1.
+ //
+ // Note that we don't worry about the opposite situation here
+ // (when BB2 is lighter than BB1). We will deal with this
+ // during the propagation phase. Right now, we just want to
+ // make sure that BB1 has the largest weight of all the
+ // members of its equivalence set.
+ unsigned &BB1Weight = BlockWeights[BB1];
+ unsigned &BB2Weight = BlockWeights[BB2];
+ BB1Weight = std::max(BB1Weight, BB2Weight);
+ }
+ }
+}
+
+/// \brief Find equivalence classes.
+///
+/// Since samples may be missing from blocks, we can fill in the gaps by setting
+/// the weights of all the blocks in the same equivalence class to the same
+/// weight. To compute the concept of equivalence, we use dominance and loop
+/// information. Two blocks B1 and B2 are in the same equivalence class if B1
+/// dominates B2, B2 post-dominates B1 and both are in the same loop.
+///
+/// \param F The function to query.
+void SampleProfileLoader::findEquivalenceClasses(Function &F) {
+ SmallVector<BasicBlock *, 8> DominatedBBs;
+ DEBUG(dbgs() << "\nBlock equivalence classes\n");
+ // Find equivalence sets based on dominance and post-dominance information.
+ for (auto &BB : F) {
+ BasicBlock *BB1 = &BB;
+
+ // Compute BB1's equivalence class once.
+ if (EquivalenceClass.count(BB1)) {
+ DEBUG(printBlockEquivalence(dbgs(), BB1));
+ continue;
+ }
+
+ // By default, blocks are in their own equivalence class.
+ EquivalenceClass[BB1] = BB1;
+
+ // Traverse all the blocks dominated by BB1. We are looking for
+ // every basic block BB2 such that:
+ //
+ // 1- BB1 dominates BB2.
+ // 2- BB2 post-dominates BB1.
+ // 3- BB1 and BB2 are in the same loop nest.
+ //
+ // If all those conditions hold, it means that BB2 is executed
+ // as many times as BB1, so they are placed in the same equivalence
+ // class by making BB2's equivalence class be BB1.
+ DominatedBBs.clear();
+ DT->getDescendants(BB1, DominatedBBs);
+ findEquivalencesFor(BB1, DominatedBBs, PDT->DT);
+
+ // Repeat the same logic for all the blocks post-dominated by BB1.
+ // We are looking for every basic block BB2 such that:
+ //
+ // 1- BB1 post-dominates BB2.
+ // 2- BB2 dominates BB1.
+ // 3- BB1 and BB2 are in the same loop nest.
+ //
+ // If all those conditions hold, BB2's equivalence class is BB1.
+ DominatedBBs.clear();
+ PDT->getDescendants(BB1, DominatedBBs);
+ findEquivalencesFor(BB1, DominatedBBs, DT);
+
+ DEBUG(printBlockEquivalence(dbgs(), BB1));
+ }
+
+ // Assign weights to equivalence classes.
+ //
+ // All the basic blocks in the same equivalence class will execute
+ // the same number of times. Since we know that the head block in
+ // each equivalence class has the largest weight, assign that weight
+ // to all the blocks in that equivalence class.
+ DEBUG(dbgs() << "\nAssign the same weight to all blocks in the same class\n");
+ for (auto &BI : F) {
+ BasicBlock *BB = &BI;
+ BasicBlock *EquivBB = EquivalenceClass[BB];
+ if (BB != EquivBB)
+ BlockWeights[BB] = BlockWeights[EquivBB];
+ DEBUG(printBlockWeight(dbgs(), BB));
+ }
+}
+
+/// \brief Visit the given edge to decide if it has a valid weight.
+///
+/// If \p E has not been visited before, we copy to \p UnknownEdge
+/// and increment the count of unknown edges.
+///
+/// \param E Edge to visit.
+/// \param NumUnknownEdges Current number of unknown edges.
+/// \param UnknownEdge Set if E has not been visited before.
+///
+/// \returns E's weight, if known. Otherwise, return 0.
+unsigned SampleProfileLoader::visitEdge(Edge E, unsigned *NumUnknownEdges,
+ Edge *UnknownEdge) {
+ if (!VisitedEdges.count(E)) {
+ (*NumUnknownEdges)++;
+ *UnknownEdge = E;
+ return 0;
+ }
+
+ return EdgeWeights[E];
+}
+
+/// \brief Propagate weights through incoming/outgoing edges.
+///
+/// If the weight of a basic block is known, and there is only one edge
+/// with an unknown weight, we can calculate the weight of that edge.
+///
+/// Similarly, if all the edges have a known count, we can calculate the
+/// count of the basic block, if needed.
+///
+/// \param F Function to process.
+///
+/// \returns True if new weights were assigned to edges or blocks.
+bool SampleProfileLoader::propagateThroughEdges(Function &F) {
+ bool Changed = false;
+ DEBUG(dbgs() << "\nPropagation through edges\n");
+ for (auto &BI : F) {
+ BasicBlock *BB = &BI;
+
+ // Visit all the predecessor and successor edges to determine
+ // which ones have a weight assigned already. Note that it doesn't
+ // matter that we only keep track of a single unknown edge. The
+ // only case we are interested in handling is when only a single
+ // edge is unknown (see setEdgeOrBlockWeight).
+ for (unsigned i = 0; i < 2; i++) {
+ unsigned TotalWeight = 0;
+ unsigned NumUnknownEdges = 0;
+ Edge UnknownEdge, SelfReferentialEdge;
+
+ if (i == 0) {
+ // First, visit all predecessor edges.
+ for (auto *Pred : Predecessors[BB]) {
+ Edge E = std::make_pair(Pred, BB);
+ TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
+ if (E.first == E.second)
+ SelfReferentialEdge = E;
+ }
+ } else {
+ // On the second round, visit all successor edges.
+ for (auto *Succ : Successors[BB]) {
+ Edge E = std::make_pair(BB, Succ);
+ TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
+ }
+ }
+
+ // After visiting all the edges, there are three cases that we
+ // can handle immediately:
+ //
+ // - All the edge weights are known (i.e., NumUnknownEdges == 0).
+ // In this case, we simply check that the sum of all the edges
+ // is the same as BB's weight. If not, we change BB's weight
+ // to match. Additionally, if BB had not been visited before,
+ // we mark it visited.
+ //
+ // - Only one edge is unknown and BB has already been visited.
+ // In this case, we can compute the weight of the edge by
+ // subtracting the total block weight from all the known
+ // edge weights. If the edges weight more than BB, then the
+ // edge of the last remaining edge is set to zero.
+ //
+ // - There exists a self-referential edge and the weight of BB is
+ // known. In this case, this edge can be based on BB's weight.
+ // We add up all the other known edges and set the weight on
+ // the self-referential edge as we did in the previous case.
+ //
+ // In any other case, we must continue iterating. Eventually,
+ // all edges will get a weight, or iteration will stop when
+ // it reaches SampleProfileMaxPropagateIterations.
+ if (NumUnknownEdges <= 1) {
+ unsigned &BBWeight = BlockWeights[BB];
+ if (NumUnknownEdges == 0) {
+ // If we already know the weight of all edges, the weight of the
+ // basic block can be computed. It should be no larger than the sum
+ // of all edge weights.
+ if (TotalWeight > BBWeight) {
+ BBWeight = TotalWeight;
+ Changed = true;
+ DEBUG(dbgs() << "All edge weights for " << BB->getName()
+ << " known. Set weight for block: ";
+ printBlockWeight(dbgs(), BB););
+ }
+ if (VisitedBlocks.insert(BB).second)
+ Changed = true;
+ } else if (NumUnknownEdges == 1 && VisitedBlocks.count(BB)) {
+ // If there is a single unknown edge and the block has been
+ // visited, then we can compute E's weight.
+ if (BBWeight >= TotalWeight)
+ EdgeWeights[UnknownEdge] = BBWeight - TotalWeight;
+ else
+ EdgeWeights[UnknownEdge] = 0;
+ VisitedEdges.insert(UnknownEdge);
+ Changed = true;
+ DEBUG(dbgs() << "Set weight for edge: ";
+ printEdgeWeight(dbgs(), UnknownEdge));
+ }
+ } else if (SelfReferentialEdge.first && VisitedBlocks.count(BB)) {
+ unsigned &BBWeight = BlockWeights[BB];
+ // We have a self-referential edge and the weight of BB is known.
+ if (BBWeight >= TotalWeight)
+ EdgeWeights[SelfReferentialEdge] = BBWeight - TotalWeight;
+ else
+ EdgeWeights[SelfReferentialEdge] = 0;
+ VisitedEdges.insert(SelfReferentialEdge);
+ Changed = true;
+ DEBUG(dbgs() << "Set self-referential edge weight to: ";
+ printEdgeWeight(dbgs(), SelfReferentialEdge));
+ }
+ }
+ }
+
+ return Changed;
+}
+
+/// \brief Build in/out edge lists for each basic block in the CFG.
+///
+/// We are interested in unique edges. If a block B1 has multiple
+/// edges to another block B2, we only add a single B1->B2 edge.
+void SampleProfileLoader::buildEdges(Function &F) {
+ for (auto &BI : F) {
+ BasicBlock *B1 = &BI;
+
+ // Add predecessors for B1.
+ SmallPtrSet<BasicBlock *, 16> Visited;
+ if (!Predecessors[B1].empty())
+ llvm_unreachable("Found a stale predecessors list in a basic block.");
+ for (pred_iterator PI = pred_begin(B1), PE = pred_end(B1); PI != PE; ++PI) {
+ BasicBlock *B2 = *PI;
+ if (Visited.insert(B2).second)
+ Predecessors[B1].push_back(B2);
+ }
+
+ // Add successors for B1.
+ Visited.clear();
+ if (!Successors[B1].empty())
+ llvm_unreachable("Found a stale successors list in a basic block.");
+ for (succ_iterator SI = succ_begin(B1), SE = succ_end(B1); SI != SE; ++SI) {
+ BasicBlock *B2 = *SI;
+ if (Visited.insert(B2).second)
+ Successors[B1].push_back(B2);
+ }
+ }
+}
+
+/// \brief Propagate weights into edges
+///
+/// The following rules are applied to every block BB in the CFG:
+///
+/// - If BB has a single predecessor/successor, then the weight
+/// of that edge is the weight of the block.
+///
+/// - If all incoming or outgoing edges are known except one, and the
+/// weight of the block is already known, the weight of the unknown
+/// edge will be the weight of the block minus the sum of all the known
+/// edges. If the sum of all the known edges is larger than BB's weight,
+/// we set the unknown edge weight to zero.
+///
+/// - If there is a self-referential edge, and the weight of the block is
+/// known, the weight for that edge is set to the weight of the block
+/// minus the weight of the other incoming edges to that block (if
+/// known).
+void SampleProfileLoader::propagateWeights(Function &F) {
+ bool Changed = true;
+ unsigned i = 0;
+
+ // Add an entry count to the function using the samples gathered
+ // at the function entry.
+ F.setEntryCount(Samples->getHeadSamples());
+
+ // Before propagation starts, build, for each block, a list of
+ // unique predecessors and successors. This is necessary to handle
+ // identical edges in multiway branches. Since we visit all blocks and all
+ // edges of the CFG, it is cleaner to build these lists once at the start
+ // of the pass.
+ buildEdges(F);
+
+ // Propagate until we converge or we go past the iteration limit.
+ while (Changed && i++ < SampleProfileMaxPropagateIterations) {
+ Changed = propagateThroughEdges(F);
+ }
+
+ // Generate MD_prof metadata for every branch instruction using the
+ // edge weights computed during propagation.
+ DEBUG(dbgs() << "\nPropagation complete. Setting branch weights\n");
+ MDBuilder MDB(F.getContext());
+ for (auto &BI : F) {
+ BasicBlock *BB = &BI;
+ TerminatorInst *TI = BB->getTerminator();
+ if (TI->getNumSuccessors() == 1)
+ continue;
+ if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
+ continue;
+
+ DEBUG(dbgs() << "\nGetting weights for branch at line "
+ << TI->getDebugLoc().getLine() << ".\n");
+ SmallVector<unsigned, 4> Weights;
+ bool AllWeightsZero = true;
+ for (unsigned I = 0; I < TI->getNumSuccessors(); ++I) {
+ BasicBlock *Succ = TI->getSuccessor(I);
+ Edge E = std::make_pair(BB, Succ);
+ unsigned Weight = EdgeWeights[E];
+ DEBUG(dbgs() << "\t"; printEdgeWeight(dbgs(), E));
+ Weights.push_back(Weight);
+ if (Weight != 0)
+ AllWeightsZero = false;
+ }
+
+ // Only set weights if there is at least one non-zero weight.
+ // In any other case, let the analyzer set weights.
+ if (!AllWeightsZero) {
+ DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n");
+ TI->setMetadata(llvm::LLVMContext::MD_prof,
+ MDB.createBranchWeights(Weights));
+ } else {
+ DEBUG(dbgs() << "SKIPPED. All branch weights are zero.\n");
+ }
+ }
+}
+
+/// \brief Get the line number for the function header.
+///
+/// This looks up function \p F in the current compilation unit and
+/// retrieves the line number where the function is defined. This is
+/// line 0 for all the samples read from the profile file. Every line
+/// number is relative to this line.
+///
+/// \param F Function object to query.
+///
+/// \returns the line number where \p F is defined. If it returns 0,
+/// it means that there is no debug information available for \p F.
+unsigned SampleProfileLoader::getFunctionLoc(Function &F) {
+ if (DISubprogram *S = getDISubprogram(&F))
+ return S->getLine();
+
+ // If could not find the start of \p F, emit a diagnostic to inform the user
+ // about the missed opportunity.
+ F.getContext().diagnose(DiagnosticInfoSampleProfile(
+ "No debug information found in function " + F.getName() +
+ ": Function profile not used",
+ DS_Warning));
+ return 0;
+}
+
+/// \brief Generate branch weight metadata for all branches in \p F.
+///
+/// Branch weights are computed out of instruction samples using a
+/// propagation heuristic. Propagation proceeds in 3 phases:
+///
+/// 1- Assignment of block weights. All the basic blocks in the function
+/// are initial assigned the same weight as their most frequently
+/// executed instruction.
+///
+/// 2- Creation of equivalence classes. Since samples may be missing from
+/// blocks, we can fill in the gaps by setting the weights of all the
+/// blocks in the same equivalence class to the same weight. To compute
+/// the concept of equivalence, we use dominance and loop information.
+/// Two blocks B1 and B2 are in the same equivalence class if B1
+/// dominates B2, B2 post-dominates B1 and both are in the same loop.
+///
+/// 3- Propagation of block weights into edges. This uses a simple
+/// propagation heuristic. The following rules are applied to every
+/// block BB in the CFG:
+///
+/// - If BB has a single predecessor/successor, then the weight
+/// of that edge is the weight of the block.
+///
+/// - If all the edges are known except one, and the weight of the
+/// block is already known, the weight of the unknown edge will
+/// be the weight of the block minus the sum of all the known
+/// edges. If the sum of all the known edges is larger than BB's weight,
+/// we set the unknown edge weight to zero.
+///
+/// - If there is a self-referential edge, and the weight of the block is
+/// known, the weight for that edge is set to the weight of the block
+/// minus the weight of the other incoming edges to that block (if
+/// known).
+///
+/// Since this propagation is not guaranteed to finalize for every CFG, we
+/// only allow it to proceed for a limited number of iterations (controlled
+/// by -sample-profile-max-propagate-iterations).
+///
+/// FIXME: Try to replace this propagation heuristic with a scheme
+/// that is guaranteed to finalize. A work-list approach similar to
+/// the standard value propagation algorithm used by SSA-CCP might
+/// work here.
+///
+/// Once all the branch weights are computed, we emit the MD_prof
+/// metadata on BB using the computed values for each of its branches.
+///
+/// \param F The function to query.
+///
+/// \returns true if \p F was modified. Returns false, otherwise.
+bool SampleProfileLoader::emitAnnotations(Function &F) {
+ bool Changed = false;
+
+ // Initialize invariants used during computation and propagation.
+ HeaderLineno = getFunctionLoc(F);
+ if (HeaderLineno == 0)
+ return false;
+
+ DEBUG(dbgs() << "Line number for the first instruction in " << F.getName()
+ << ": " << HeaderLineno << "\n");
+
+ // Compute basic block weights.
+ Changed |= computeBlockWeights(F);
+
+ if (Changed) {
+ // Find equivalence classes.
+ findEquivalenceClasses(F);
+
+ // Propagate weights to all edges.
+ propagateWeights(F);
+ }
+
+ return Changed;
+}
+
+char SampleProfileLoader::ID = 0;
+INITIALIZE_PASS_BEGIN(SampleProfileLoader, "sample-profile",
+ "Sample Profile loader", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(PostDominatorTree)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(AddDiscriminators)
+INITIALIZE_PASS_END(SampleProfileLoader, "sample-profile",
+ "Sample Profile loader", false, false)
+
+bool SampleProfileLoader::doInitialization(Module &M) {
+ auto& Ctx = M.getContext();
+ auto ReaderOrErr = SampleProfileReader::create(Filename, Ctx);
+ if (std::error_code EC = ReaderOrErr.getError()) {
+ std::string Msg = "Could not open profile: " + EC.message();
+ Ctx.diagnose(DiagnosticInfoSampleProfile(Filename.data(), Msg));
+ return false;
+ }
+ Reader = std::move(ReaderOrErr.get());
+ ProfileIsValid = (Reader->read() == sampleprof_error::success);
+ return true;
+}
+
+ModulePass *llvm::createSampleProfileLoaderPass() {
+ return new SampleProfileLoader(SampleProfileFile);
+}
+
+ModulePass *llvm::createSampleProfileLoaderPass(StringRef Name) {
+ return new SampleProfileLoader(Name);
+}
+
+bool SampleProfileLoader::runOnModule(Module &M) {
+ bool retval = false;
+ for (auto &F : M)
+ if (!F.isDeclaration())
+ retval |= runOnFunction(F);
+ return retval;
+}
+
+bool SampleProfileLoader::runOnFunction(Function &F) {
+ if (!ProfileIsValid)
+ return false;
+
+ DT = &getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
+ PDT = &getAnalysis<PostDominatorTree>(F);
+ LI = &getAnalysis<LoopInfoWrapperPass>(F).getLoopInfo();
+ Ctx = &F.getParent()->getContext();
+ Samples = Reader->getSamplesFor(F);
+ if (!Samples->empty())
+ return emitAnnotations(F);
+ return false;
+}
RewriteStatepointsForGC.cpp
SCCP.cpp
SROA.cpp
- SampleProfile.cpp
Scalar.cpp
ScalarReplAggregates.cpp
Scalarizer.cpp
+++ /dev/null
-//===- SampleProfile.cpp - Incorporate sample profiles into the IR --------===//
-//
-// The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file implements the SampleProfileLoader transformation. This pass
-// reads a profile file generated by a sampling profiler (e.g. Linux Perf -
-// http://perf.wiki.kernel.org/) and generates IR metadata to reflect the
-// profile information in the given profile.
-//
-// This pass generates branch weight annotations on the IR:
-//
-// - prof: Represents branch weights. This annotation is added to branches
-// to indicate the weights of each edge coming out of the branch.
-// The weight of each edge is the weight of the target block for
-// that edge. The weight of a block B is computed as the maximum
-// number of samples found in B.
-//
-//===----------------------------------------------------------------------===//
-
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/SmallPtrSet.h"
-#include "llvm/ADT/SmallSet.h"
-#include "llvm/ADT/StringRef.h"
-#include "llvm/Analysis/LoopInfo.h"
-#include "llvm/Analysis/PostDominators.h"
-#include "llvm/IR/Constants.h"
-#include "llvm/IR/DebugInfo.h"
-#include "llvm/IR/DiagnosticInfo.h"
-#include "llvm/IR/Dominators.h"
-#include "llvm/IR/Function.h"
-#include "llvm/IR/InstIterator.h"
-#include "llvm/IR/Instructions.h"
-#include "llvm/IR/LLVMContext.h"
-#include "llvm/IR/MDBuilder.h"
-#include "llvm/IR/Metadata.h"
-#include "llvm/IR/Module.h"
-#include "llvm/Pass.h"
-#include "llvm/ProfileData/SampleProfReader.h"
-#include "llvm/Support/CommandLine.h"
-#include "llvm/Support/Debug.h"
-#include "llvm/Support/raw_ostream.h"
-#include <cctype>
-
-using namespace llvm;
-using namespace sampleprof;
-
-#define DEBUG_TYPE "sample-profile"
-
-// Command line option to specify the file to read samples from. This is
-// mainly used for debugging.
-static cl::opt<std::string> SampleProfileFile(
- "sample-profile-file", cl::init(""), cl::value_desc("filename"),
- cl::desc("Profile file loaded by -sample-profile"), cl::Hidden);
-static cl::opt<unsigned> SampleProfileMaxPropagateIterations(
- "sample-profile-max-propagate-iterations", cl::init(100),
- cl::desc("Maximum number of iterations to go through when propagating "
- "sample block/edge weights through the CFG."));
-
-namespace {
-typedef DenseMap<BasicBlock *, unsigned> BlockWeightMap;
-typedef DenseMap<BasicBlock *, BasicBlock *> EquivalenceClassMap;
-typedef std::pair<BasicBlock *, BasicBlock *> Edge;
-typedef DenseMap<Edge, unsigned> EdgeWeightMap;
-typedef DenseMap<BasicBlock *, SmallVector<BasicBlock *, 8>> BlockEdgeMap;
-
-/// \brief Sample profile pass.
-///
-/// This pass reads profile data from the file specified by
-/// -sample-profile-file and annotates every affected function with the
-/// profile information found in that file.
-class SampleProfileLoader : public FunctionPass {
-public:
- // Class identification, replacement for typeinfo
- static char ID;
-
- SampleProfileLoader(StringRef Name = SampleProfileFile)
- : FunctionPass(ID), DT(nullptr), PDT(nullptr), LI(nullptr), Ctx(nullptr),
- Reader(), Samples(nullptr), Filename(Name), ProfileIsValid(false) {
- initializeSampleProfileLoaderPass(*PassRegistry::getPassRegistry());
- }
-
- bool doInitialization(Module &M) override;
-
- void dump() { Reader->dump(); }
-
- const char *getPassName() const override { return "Sample profile pass"; }
-
- bool runOnFunction(Function &F) override;
-
- void getAnalysisUsage(AnalysisUsage &AU) const override {
- AU.setPreservesCFG();
- AU.addRequired<LoopInfoWrapperPass>();
- AU.addRequired<DominatorTreeWrapperPass>();
- AU.addRequired<PostDominatorTree>();
- }
-
-protected:
- unsigned getFunctionLoc(Function &F);
- bool emitAnnotations(Function &F);
- unsigned getInstWeight(Instruction &I);
- unsigned getBlockWeight(BasicBlock *BB);
- void printEdgeWeight(raw_ostream &OS, Edge E);
- void printBlockWeight(raw_ostream &OS, BasicBlock *BB);
- void printBlockEquivalence(raw_ostream &OS, BasicBlock *BB);
- bool computeBlockWeights(Function &F);
- void findEquivalenceClasses(Function &F);
- void findEquivalencesFor(BasicBlock *BB1,
- SmallVector<BasicBlock *, 8> Descendants,
- DominatorTreeBase<BasicBlock> *DomTree);
- void propagateWeights(Function &F);
- unsigned visitEdge(Edge E, unsigned *NumUnknownEdges, Edge *UnknownEdge);
- void buildEdges(Function &F);
- bool propagateThroughEdges(Function &F);
-
- /// \brief Line number for the function header. Used to compute absolute
- /// line numbers from the relative line numbers found in the profile.
- unsigned HeaderLineno;
-
- /// \brief Map basic blocks to their computed weights.
- ///
- /// The weight of a basic block is defined to be the maximum
- /// of all the instruction weights in that block.
- BlockWeightMap BlockWeights;
-
- /// \brief Map edges to their computed weights.
- ///
- /// Edge weights are computed by propagating basic block weights in
- /// SampleProfile::propagateWeights.
- EdgeWeightMap EdgeWeights;
-
- /// \brief Set of visited blocks during propagation.
- SmallPtrSet<BasicBlock *, 128> VisitedBlocks;
-
- /// \brief Set of visited edges during propagation.
- SmallSet<Edge, 128> VisitedEdges;
-
- /// \brief Equivalence classes for block weights.
- ///
- /// Two blocks BB1 and BB2 are in the same equivalence class if they
- /// dominate and post-dominate each other, and they are in the same loop
- /// nest. When this happens, the two blocks are guaranteed to execute
- /// the same number of times.
- EquivalenceClassMap EquivalenceClass;
-
- /// \brief Dominance, post-dominance and loop information.
- DominatorTree *DT;
- PostDominatorTree *PDT;
- LoopInfo *LI;
-
- /// \brief Predecessors for each basic block in the CFG.
- BlockEdgeMap Predecessors;
-
- /// \brief Successors for each basic block in the CFG.
- BlockEdgeMap Successors;
-
- /// \brief LLVM context holding the debug data we need.
- LLVMContext *Ctx;
-
- /// \brief Profile reader object.
- std::unique_ptr<SampleProfileReader> Reader;
-
- /// \brief Samples collected for the body of this function.
- FunctionSamples *Samples;
-
- /// \brief Name of the profile file to load.
- StringRef Filename;
-
- /// \brief Flag indicating whether the profile input loaded successfully.
- bool ProfileIsValid;
-};
-}
-
-/// \brief Print the weight of edge \p E on stream \p OS.
-///
-/// \param OS Stream to emit the output to.
-/// \param E Edge to print.
-void SampleProfileLoader::printEdgeWeight(raw_ostream &OS, Edge E) {
- OS << "weight[" << E.first->getName() << "->" << E.second->getName()
- << "]: " << EdgeWeights[E] << "\n";
-}
-
-/// \brief Print the equivalence class of block \p BB on stream \p OS.
-///
-/// \param OS Stream to emit the output to.
-/// \param BB Block to print.
-void SampleProfileLoader::printBlockEquivalence(raw_ostream &OS,
- BasicBlock *BB) {
- BasicBlock *Equiv = EquivalenceClass[BB];
- OS << "equivalence[" << BB->getName()
- << "]: " << ((Equiv) ? EquivalenceClass[BB]->getName() : "NONE") << "\n";
-}
-
-/// \brief Print the weight of block \p BB on stream \p OS.
-///
-/// \param OS Stream to emit the output to.
-/// \param BB Block to print.
-void SampleProfileLoader::printBlockWeight(raw_ostream &OS, BasicBlock *BB) {
- OS << "weight[" << BB->getName() << "]: " << BlockWeights[BB] << "\n";
-}
-
-/// \brief Get the weight for an instruction.
-///
-/// The "weight" of an instruction \p Inst is the number of samples
-/// collected on that instruction at runtime. To retrieve it, we
-/// need to compute the line number of \p Inst relative to the start of its
-/// function. We use HeaderLineno to compute the offset. We then
-/// look up the samples collected for \p Inst using BodySamples.
-///
-/// \param Inst Instruction to query.
-///
-/// \returns The profiled weight of I.
-unsigned SampleProfileLoader::getInstWeight(Instruction &Inst) {
- DebugLoc DLoc = Inst.getDebugLoc();
- if (!DLoc)
- return 0;
-
- unsigned Lineno = DLoc.getLine();
- if (Lineno < HeaderLineno)
- return 0;
-
- const DILocation *DIL = DLoc;
- int LOffset = Lineno - HeaderLineno;
- unsigned Discriminator = DIL->getDiscriminator();
- unsigned Weight = Samples->samplesAt(LOffset, Discriminator);
- DEBUG(dbgs() << " " << Lineno << "." << Discriminator << ":" << Inst
- << " (line offset: " << LOffset << "." << Discriminator
- << " - weight: " << Weight << ")\n");
- return Weight;
-}
-
-/// \brief Compute the weight of a basic block.
-///
-/// The weight of basic block \p BB is the maximum weight of all the
-/// instructions in BB. The weight of \p BB is computed and cached in
-/// the BlockWeights map.
-///
-/// \param BB The basic block to query.
-///
-/// \returns The computed weight of BB.
-unsigned SampleProfileLoader::getBlockWeight(BasicBlock *BB) {
- // If we've computed BB's weight before, return it.
- std::pair<BlockWeightMap::iterator, bool> Entry =
- BlockWeights.insert(std::make_pair(BB, 0));
- if (!Entry.second)
- return Entry.first->second;
-
- // Otherwise, compute and cache BB's weight.
- unsigned Weight = 0;
- for (auto &I : BB->getInstList()) {
- unsigned InstWeight = getInstWeight(I);
- if (InstWeight > Weight)
- Weight = InstWeight;
- }
- Entry.first->second = Weight;
- return Weight;
-}
-
-/// \brief Compute and store the weights of every basic block.
-///
-/// This populates the BlockWeights map by computing
-/// the weights of every basic block in the CFG.
-///
-/// \param F The function to query.
-bool SampleProfileLoader::computeBlockWeights(Function &F) {
- bool Changed = false;
- DEBUG(dbgs() << "Block weights\n");
- for (auto &BB : F) {
- unsigned Weight = getBlockWeight(&BB);
- Changed |= (Weight > 0);
- DEBUG(printBlockWeight(dbgs(), &BB));
- }
-
- return Changed;
-}
-
-/// \brief Find equivalence classes for the given block.
-///
-/// This finds all the blocks that are guaranteed to execute the same
-/// number of times as \p BB1. To do this, it traverses all the
-/// descendants of \p BB1 in the dominator or post-dominator tree.
-///
-/// A block BB2 will be in the same equivalence class as \p BB1 if
-/// the following holds:
-///
-/// 1- \p BB1 is a descendant of BB2 in the opposite tree. So, if BB2
-/// is a descendant of \p BB1 in the dominator tree, then BB2 should
-/// dominate BB1 in the post-dominator tree.
-///
-/// 2- Both BB2 and \p BB1 must be in the same loop.
-///
-/// For every block BB2 that meets those two requirements, we set BB2's
-/// equivalence class to \p BB1.
-///
-/// \param BB1 Block to check.
-/// \param Descendants Descendants of \p BB1 in either the dom or pdom tree.
-/// \param DomTree Opposite dominator tree. If \p Descendants is filled
-/// with blocks from \p BB1's dominator tree, then
-/// this is the post-dominator tree, and vice versa.
-void SampleProfileLoader::findEquivalencesFor(
- BasicBlock *BB1, SmallVector<BasicBlock *, 8> Descendants,
- DominatorTreeBase<BasicBlock> *DomTree) {
- for (auto *BB2 : Descendants) {
- bool IsDomParent = DomTree->dominates(BB2, BB1);
- bool IsInSameLoop = LI->getLoopFor(BB1) == LI->getLoopFor(BB2);
- if (BB1 != BB2 && VisitedBlocks.insert(BB2).second && IsDomParent &&
- IsInSameLoop) {
- EquivalenceClass[BB2] = BB1;
-
- // If BB2 is heavier than BB1, make BB2 have the same weight
- // as BB1.
- //
- // Note that we don't worry about the opposite situation here
- // (when BB2 is lighter than BB1). We will deal with this
- // during the propagation phase. Right now, we just want to
- // make sure that BB1 has the largest weight of all the
- // members of its equivalence set.
- unsigned &BB1Weight = BlockWeights[BB1];
- unsigned &BB2Weight = BlockWeights[BB2];
- BB1Weight = std::max(BB1Weight, BB2Weight);
- }
- }
-}
-
-/// \brief Find equivalence classes.
-///
-/// Since samples may be missing from blocks, we can fill in the gaps by setting
-/// the weights of all the blocks in the same equivalence class to the same
-/// weight. To compute the concept of equivalence, we use dominance and loop
-/// information. Two blocks B1 and B2 are in the same equivalence class if B1
-/// dominates B2, B2 post-dominates B1 and both are in the same loop.
-///
-/// \param F The function to query.
-void SampleProfileLoader::findEquivalenceClasses(Function &F) {
- SmallVector<BasicBlock *, 8> DominatedBBs;
- DEBUG(dbgs() << "\nBlock equivalence classes\n");
- // Find equivalence sets based on dominance and post-dominance information.
- for (auto &BB : F) {
- BasicBlock *BB1 = &BB;
-
- // Compute BB1's equivalence class once.
- if (EquivalenceClass.count(BB1)) {
- DEBUG(printBlockEquivalence(dbgs(), BB1));
- continue;
- }
-
- // By default, blocks are in their own equivalence class.
- EquivalenceClass[BB1] = BB1;
-
- // Traverse all the blocks dominated by BB1. We are looking for
- // every basic block BB2 such that:
- //
- // 1- BB1 dominates BB2.
- // 2- BB2 post-dominates BB1.
- // 3- BB1 and BB2 are in the same loop nest.
- //
- // If all those conditions hold, it means that BB2 is executed
- // as many times as BB1, so they are placed in the same equivalence
- // class by making BB2's equivalence class be BB1.
- DominatedBBs.clear();
- DT->getDescendants(BB1, DominatedBBs);
- findEquivalencesFor(BB1, DominatedBBs, PDT->DT);
-
- // Repeat the same logic for all the blocks post-dominated by BB1.
- // We are looking for every basic block BB2 such that:
- //
- // 1- BB1 post-dominates BB2.
- // 2- BB2 dominates BB1.
- // 3- BB1 and BB2 are in the same loop nest.
- //
- // If all those conditions hold, BB2's equivalence class is BB1.
- DominatedBBs.clear();
- PDT->getDescendants(BB1, DominatedBBs);
- findEquivalencesFor(BB1, DominatedBBs, DT);
-
- DEBUG(printBlockEquivalence(dbgs(), BB1));
- }
-
- // Assign weights to equivalence classes.
- //
- // All the basic blocks in the same equivalence class will execute
- // the same number of times. Since we know that the head block in
- // each equivalence class has the largest weight, assign that weight
- // to all the blocks in that equivalence class.
- DEBUG(dbgs() << "\nAssign the same weight to all blocks in the same class\n");
- for (auto &BI : F) {
- BasicBlock *BB = &BI;
- BasicBlock *EquivBB = EquivalenceClass[BB];
- if (BB != EquivBB)
- BlockWeights[BB] = BlockWeights[EquivBB];
- DEBUG(printBlockWeight(dbgs(), BB));
- }
-}
-
-/// \brief Visit the given edge to decide if it has a valid weight.
-///
-/// If \p E has not been visited before, we copy to \p UnknownEdge
-/// and increment the count of unknown edges.
-///
-/// \param E Edge to visit.
-/// \param NumUnknownEdges Current number of unknown edges.
-/// \param UnknownEdge Set if E has not been visited before.
-///
-/// \returns E's weight, if known. Otherwise, return 0.
-unsigned SampleProfileLoader::visitEdge(Edge E, unsigned *NumUnknownEdges,
- Edge *UnknownEdge) {
- if (!VisitedEdges.count(E)) {
- (*NumUnknownEdges)++;
- *UnknownEdge = E;
- return 0;
- }
-
- return EdgeWeights[E];
-}
-
-/// \brief Propagate weights through incoming/outgoing edges.
-///
-/// If the weight of a basic block is known, and there is only one edge
-/// with an unknown weight, we can calculate the weight of that edge.
-///
-/// Similarly, if all the edges have a known count, we can calculate the
-/// count of the basic block, if needed.
-///
-/// \param F Function to process.
-///
-/// \returns True if new weights were assigned to edges or blocks.
-bool SampleProfileLoader::propagateThroughEdges(Function &F) {
- bool Changed = false;
- DEBUG(dbgs() << "\nPropagation through edges\n");
- for (auto &BI : F) {
- BasicBlock *BB = &BI;
-
- // Visit all the predecessor and successor edges to determine
- // which ones have a weight assigned already. Note that it doesn't
- // matter that we only keep track of a single unknown edge. The
- // only case we are interested in handling is when only a single
- // edge is unknown (see setEdgeOrBlockWeight).
- for (unsigned i = 0; i < 2; i++) {
- unsigned TotalWeight = 0;
- unsigned NumUnknownEdges = 0;
- Edge UnknownEdge, SelfReferentialEdge;
-
- if (i == 0) {
- // First, visit all predecessor edges.
- for (auto *Pred : Predecessors[BB]) {
- Edge E = std::make_pair(Pred, BB);
- TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
- if (E.first == E.second)
- SelfReferentialEdge = E;
- }
- } else {
- // On the second round, visit all successor edges.
- for (auto *Succ : Successors[BB]) {
- Edge E = std::make_pair(BB, Succ);
- TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge);
- }
- }
-
- // After visiting all the edges, there are three cases that we
- // can handle immediately:
- //
- // - All the edge weights are known (i.e., NumUnknownEdges == 0).
- // In this case, we simply check that the sum of all the edges
- // is the same as BB's weight. If not, we change BB's weight
- // to match. Additionally, if BB had not been visited before,
- // we mark it visited.
- //
- // - Only one edge is unknown and BB has already been visited.
- // In this case, we can compute the weight of the edge by
- // subtracting the total block weight from all the known
- // edge weights. If the edges weight more than BB, then the
- // edge of the last remaining edge is set to zero.
- //
- // - There exists a self-referential edge and the weight of BB is
- // known. In this case, this edge can be based on BB's weight.
- // We add up all the other known edges and set the weight on
- // the self-referential edge as we did in the previous case.
- //
- // In any other case, we must continue iterating. Eventually,
- // all edges will get a weight, or iteration will stop when
- // it reaches SampleProfileMaxPropagateIterations.
- if (NumUnknownEdges <= 1) {
- unsigned &BBWeight = BlockWeights[BB];
- if (NumUnknownEdges == 0) {
- // If we already know the weight of all edges, the weight of the
- // basic block can be computed. It should be no larger than the sum
- // of all edge weights.
- if (TotalWeight > BBWeight) {
- BBWeight = TotalWeight;
- Changed = true;
- DEBUG(dbgs() << "All edge weights for " << BB->getName()
- << " known. Set weight for block: ";
- printBlockWeight(dbgs(), BB););
- }
- if (VisitedBlocks.insert(BB).second)
- Changed = true;
- } else if (NumUnknownEdges == 1 && VisitedBlocks.count(BB)) {
- // If there is a single unknown edge and the block has been
- // visited, then we can compute E's weight.
- if (BBWeight >= TotalWeight)
- EdgeWeights[UnknownEdge] = BBWeight - TotalWeight;
- else
- EdgeWeights[UnknownEdge] = 0;
- VisitedEdges.insert(UnknownEdge);
- Changed = true;
- DEBUG(dbgs() << "Set weight for edge: ";
- printEdgeWeight(dbgs(), UnknownEdge));
- }
- } else if (SelfReferentialEdge.first && VisitedBlocks.count(BB)) {
- unsigned &BBWeight = BlockWeights[BB];
- // We have a self-referential edge and the weight of BB is known.
- if (BBWeight >= TotalWeight)
- EdgeWeights[SelfReferentialEdge] = BBWeight - TotalWeight;
- else
- EdgeWeights[SelfReferentialEdge] = 0;
- VisitedEdges.insert(SelfReferentialEdge);
- Changed = true;
- DEBUG(dbgs() << "Set self-referential edge weight to: ";
- printEdgeWeight(dbgs(), SelfReferentialEdge));
- }
- }
- }
-
- return Changed;
-}
-
-/// \brief Build in/out edge lists for each basic block in the CFG.
-///
-/// We are interested in unique edges. If a block B1 has multiple
-/// edges to another block B2, we only add a single B1->B2 edge.
-void SampleProfileLoader::buildEdges(Function &F) {
- for (auto &BI : F) {
- BasicBlock *B1 = &BI;
-
- // Add predecessors for B1.
- SmallPtrSet<BasicBlock *, 16> Visited;
- if (!Predecessors[B1].empty())
- llvm_unreachable("Found a stale predecessors list in a basic block.");
- for (pred_iterator PI = pred_begin(B1), PE = pred_end(B1); PI != PE; ++PI) {
- BasicBlock *B2 = *PI;
- if (Visited.insert(B2).second)
- Predecessors[B1].push_back(B2);
- }
-
- // Add successors for B1.
- Visited.clear();
- if (!Successors[B1].empty())
- llvm_unreachable("Found a stale successors list in a basic block.");
- for (succ_iterator SI = succ_begin(B1), SE = succ_end(B1); SI != SE; ++SI) {
- BasicBlock *B2 = *SI;
- if (Visited.insert(B2).second)
- Successors[B1].push_back(B2);
- }
- }
-}
-
-/// \brief Propagate weights into edges
-///
-/// The following rules are applied to every block BB in the CFG:
-///
-/// - If BB has a single predecessor/successor, then the weight
-/// of that edge is the weight of the block.
-///
-/// - If all incoming or outgoing edges are known except one, and the
-/// weight of the block is already known, the weight of the unknown
-/// edge will be the weight of the block minus the sum of all the known
-/// edges. If the sum of all the known edges is larger than BB's weight,
-/// we set the unknown edge weight to zero.
-///
-/// - If there is a self-referential edge, and the weight of the block is
-/// known, the weight for that edge is set to the weight of the block
-/// minus the weight of the other incoming edges to that block (if
-/// known).
-void SampleProfileLoader::propagateWeights(Function &F) {
- bool Changed = true;
- unsigned i = 0;
-
- // Add an entry count to the function using the samples gathered
- // at the function entry.
- F.setEntryCount(Samples->getHeadSamples());
-
- // Before propagation starts, build, for each block, a list of
- // unique predecessors and successors. This is necessary to handle
- // identical edges in multiway branches. Since we visit all blocks and all
- // edges of the CFG, it is cleaner to build these lists once at the start
- // of the pass.
- buildEdges(F);
-
- // Propagate until we converge or we go past the iteration limit.
- while (Changed && i++ < SampleProfileMaxPropagateIterations) {
- Changed = propagateThroughEdges(F);
- }
-
- // Generate MD_prof metadata for every branch instruction using the
- // edge weights computed during propagation.
- DEBUG(dbgs() << "\nPropagation complete. Setting branch weights\n");
- MDBuilder MDB(F.getContext());
- for (auto &BI : F) {
- BasicBlock *BB = &BI;
- TerminatorInst *TI = BB->getTerminator();
- if (TI->getNumSuccessors() == 1)
- continue;
- if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
- continue;
-
- DEBUG(dbgs() << "\nGetting weights for branch at line "
- << TI->getDebugLoc().getLine() << ".\n");
- SmallVector<unsigned, 4> Weights;
- bool AllWeightsZero = true;
- for (unsigned I = 0; I < TI->getNumSuccessors(); ++I) {
- BasicBlock *Succ = TI->getSuccessor(I);
- Edge E = std::make_pair(BB, Succ);
- unsigned Weight = EdgeWeights[E];
- DEBUG(dbgs() << "\t"; printEdgeWeight(dbgs(), E));
- Weights.push_back(Weight);
- if (Weight != 0)
- AllWeightsZero = false;
- }
-
- // Only set weights if there is at least one non-zero weight.
- // In any other case, let the analyzer set weights.
- if (!AllWeightsZero) {
- DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n");
- TI->setMetadata(llvm::LLVMContext::MD_prof,
- MDB.createBranchWeights(Weights));
- } else {
- DEBUG(dbgs() << "SKIPPED. All branch weights are zero.\n");
- }
- }
-}
-
-/// \brief Get the line number for the function header.
-///
-/// This looks up function \p F in the current compilation unit and
-/// retrieves the line number where the function is defined. This is
-/// line 0 for all the samples read from the profile file. Every line
-/// number is relative to this line.
-///
-/// \param F Function object to query.
-///
-/// \returns the line number where \p F is defined. If it returns 0,
-/// it means that there is no debug information available for \p F.
-unsigned SampleProfileLoader::getFunctionLoc(Function &F) {
- if (DISubprogram *S = getDISubprogram(&F))
- return S->getLine();
-
- // If could not find the start of \p F, emit a diagnostic to inform the user
- // about the missed opportunity.
- F.getContext().diagnose(DiagnosticInfoSampleProfile(
- "No debug information found in function " + F.getName() +
- ": Function profile not used",
- DS_Warning));
- return 0;
-}
-
-/// \brief Generate branch weight metadata for all branches in \p F.
-///
-/// Branch weights are computed out of instruction samples using a
-/// propagation heuristic. Propagation proceeds in 3 phases:
-///
-/// 1- Assignment of block weights. All the basic blocks in the function
-/// are initial assigned the same weight as their most frequently
-/// executed instruction.
-///
-/// 2- Creation of equivalence classes. Since samples may be missing from
-/// blocks, we can fill in the gaps by setting the weights of all the
-/// blocks in the same equivalence class to the same weight. To compute
-/// the concept of equivalence, we use dominance and loop information.
-/// Two blocks B1 and B2 are in the same equivalence class if B1
-/// dominates B2, B2 post-dominates B1 and both are in the same loop.
-///
-/// 3- Propagation of block weights into edges. This uses a simple
-/// propagation heuristic. The following rules are applied to every
-/// block BB in the CFG:
-///
-/// - If BB has a single predecessor/successor, then the weight
-/// of that edge is the weight of the block.
-///
-/// - If all the edges are known except one, and the weight of the
-/// block is already known, the weight of the unknown edge will
-/// be the weight of the block minus the sum of all the known
-/// edges. If the sum of all the known edges is larger than BB's weight,
-/// we set the unknown edge weight to zero.
-///
-/// - If there is a self-referential edge, and the weight of the block is
-/// known, the weight for that edge is set to the weight of the block
-/// minus the weight of the other incoming edges to that block (if
-/// known).
-///
-/// Since this propagation is not guaranteed to finalize for every CFG, we
-/// only allow it to proceed for a limited number of iterations (controlled
-/// by -sample-profile-max-propagate-iterations).
-///
-/// FIXME: Try to replace this propagation heuristic with a scheme
-/// that is guaranteed to finalize. A work-list approach similar to
-/// the standard value propagation algorithm used by SSA-CCP might
-/// work here.
-///
-/// Once all the branch weights are computed, we emit the MD_prof
-/// metadata on BB using the computed values for each of its branches.
-///
-/// \param F The function to query.
-///
-/// \returns true if \p F was modified. Returns false, otherwise.
-bool SampleProfileLoader::emitAnnotations(Function &F) {
- bool Changed = false;
-
- // Initialize invariants used during computation and propagation.
- HeaderLineno = getFunctionLoc(F);
- if (HeaderLineno == 0)
- return false;
-
- DEBUG(dbgs() << "Line number for the first instruction in " << F.getName()
- << ": " << HeaderLineno << "\n");
-
- // Compute basic block weights.
- Changed |= computeBlockWeights(F);
-
- if (Changed) {
- // Find equivalence classes.
- findEquivalenceClasses(F);
-
- // Propagate weights to all edges.
- propagateWeights(F);
- }
-
- return Changed;
-}
-
-char SampleProfileLoader::ID = 0;
-INITIALIZE_PASS_BEGIN(SampleProfileLoader, "sample-profile",
- "Sample Profile loader", false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(PostDominatorTree)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(AddDiscriminators)
-INITIALIZE_PASS_END(SampleProfileLoader, "sample-profile",
- "Sample Profile loader", false, false)
-
-bool SampleProfileLoader::doInitialization(Module &M) {
- auto ReaderOrErr = SampleProfileReader::create(Filename, M.getContext());
- if (std::error_code EC = ReaderOrErr.getError()) {
- std::string Msg = "Could not open profile: " + EC.message();
- M.getContext().diagnose(DiagnosticInfoSampleProfile(Filename.data(), Msg));
- return false;
- }
- Reader = std::move(ReaderOrErr.get());
- ProfileIsValid = (Reader->read() == sampleprof_error::success);
- return true;
-}
-
-FunctionPass *llvm::createSampleProfileLoaderPass() {
- return new SampleProfileLoader(SampleProfileFile);
-}
-
-FunctionPass *llvm::createSampleProfileLoaderPass(StringRef Name) {
- return new SampleProfileLoader(Name);
-}
-
-bool SampleProfileLoader::runOnFunction(Function &F) {
- if (!ProfileIsValid)
- return false;
-
- DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
- PDT = &getAnalysis<PostDominatorTree>();
- LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
- Ctx = &F.getParent()->getContext();
- Samples = Reader->getSamplesFor(F);
- if (!Samples->empty())
- return emitAnnotations(F);
- return false;
-}
initializeADCEPass(Registry);
initializeBDCEPass(Registry);
initializeAlignmentFromAssumptionsPass(Registry);
- initializeSampleProfileLoaderPass(Registry);
initializeConstantHoistingPass(Registry);
initializeConstantPropagationPass(Registry);
initializeCorrelatedValuePropagationPass(Registry);
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